This is a historical question that's been bugging me for ages and I've never gotten an answer that makes sense. I apologize if this has been asked before, but I did a good bit of searching in your old posts and couldn't find it.

So how is it that cities (such as Rome) have excavated buildings underneath buildings? How did the ground 'rise up' so to speak? I hope I'm being clear enough, I just don't understand how a city could be built on top of itself.